Study offers new picture of Tahoe geology

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LAKE TAHOE " Researchers studying the history of earthquakes in the Lake Tahoe region say a large quake occurs every 2,000 to 3,000 years in the Basin, and the area is past due for another.

But don't run for the flatlands, yet. Earthquakes are nearly impossible to predict, and most of the research being conducted around the lake was for the unique purpose of tracking underwater faults located in the world's oceans.

"This was out of the box," said researcher Graham Kent. "The assumption was, could we even do this work under the water? What was neat about the Tahoe site was it's a first of a kind, and now we're taking that technology around the world."

While researchers started the study done by the Scripps Institution of Oceanography at U.C. San Diego as an experiment in underwater technology, what they found soon raised their eyebrows.

The discovered the most dangerous fault located on Tahoe's West Shore broke apart 5,000 years ago " and does so on average every couple thousand years " and if it were to break again, most likely would result in a 7-plus reading on the Richter scale. This could result in a tsunami on the lake with waves more than 30 feet high, Kent said.

The most recent large-scale quake occurred 575 year ago on the Incline Village Fault, Kent said.

"The thing to know is that folks are in the background trying to use these things and to find ways to mitigate damage," he added. "We can't stop an earthquake, but when you look at the type of acceleration of earthquake activity in the Reno area, if they were to happen in another place in the world, it could result in a lot of damage and fatalities."

An active fault is defined as one that has moved in the last 12,000 years, making the Lake Tahoe region "very active," Kent said.

The research is already being used in studies near Northern Ireland, Kent added, and that it could be used in underwater areas that recently triggered the large tsunamis in Indonesia.

For more than a decade, scientists at Scripps Institution of Oceanography at U.C. San Diego have been unraveling the history of fault ruptures below Lake Tahoe by studying one earthquake at a time.

These studies, led by a team of Scripps researchers including Kent, Neal Driscoll, Jeff Babcock and Alistair Harding, collected new data on earthquake history along three active faults in the region.

Jeff Dingler, lead author on a paper in the April online issue of Geological Society of America Bulletin (GSA Bulletin) and former Scripps Oceanography graduate student, used a high-resolution seismic imaging technique, known as CHIRP, to supply a comprehensive view of faulting beneath the lake.

Scripps' Neal Driscoll provided an unprecedented picture of deformation within the sedimentary layers that blanket the floor of Lake Tahoe, laying the groundwork for more detailed fault studies that continue today.